As integrated circuit feature sizes continue to decrease, it has become advantageous to construct metal interconnects out of copper. Copper has a low resistivity and therefore can form higher speed connections for a given wire width. However, Copper does have disadvantages that must be overcome. For example, copper is much more susceptible to oxidation during processing. Copper also tends to diffuse into adjacent materials, including dielectrics. To use copper for interconnections, therefore, it is necessary to encapsulate the copper in barrier materials.
After the copper interconnect is fabricated, a barrier layer or cap is formed thereupon, typically called a sealing layer. Typically in the art, this sealing layer (also called a cap layer, or an encapsulation layer) is formed from a material that has the highest dielectric constant value within the BEOL metalization or wiring stack and may thus adversely impact the capacitance within the BEOL metalization or wiring stack.